The present invention relates generally to the field of manufacturing processes, and more particularly, to a manufacturing processes that includes an extrusion step and a blow molding step in-line, to produce a resultant product. The present invention may be useful in the manufacturing of a multitude of different products, product shapes, product configurations, and may be used with any materials which are suitable for extrusion and blow molding processes.
Extrusions of material, especially plastic material, are well known. For example, a class of plastics, known as thermoplastic material, has been commonly extruded through extrusion equipment that is widely available. An example of such extrusion equipment is a Cincinnati Milacron Model CM80 Extruder. Those skilled in the art of extrusion of materials are well versed in the workings of extruders and the use of materials in such extruders as well as the use of various dies to produce resultant shapes at the finish point of the extruder. For example, in a customary use of extruders, raw materials are provided to the extruder along with other additives and lubricants known to those of skill in the art, then passed through the extruder and subjected to heat and compression causing the combination of materials to form a mass of flowing material that passes through one or more dies of predetermined shape. The material is pushed by the extruder through the dies and exits the dies in the desired shape, where the material is then left to cool and harden into a more rigid product. As is well known to those of skill in the art of extruding, dies may be designed to result in the formation of hollows in a finished extruded part. Extruded products having hollows simply means that the part is not solid material all the way through, but instead has a hollow section within it.
The art of blow molding and blow molding processes are also well known to those of ordinary skill in the art of blow molding. Blow molding is also associated with plastics and the use of heat and pressure to form a product having a resulted pre-determined shape. A mold is formed with the desired shape, the material is placed in the mold, and is then subjected to air pressure to blow the material into the shape of the mold. The equipment used in the blow molding process is well known to those of ordinary skill in the art.
The present invention involves the combination of an extrusion process and a blow molding process to achieve a desired end product. With the present invention, material is first extruded through one or more dies and upon exiting the die(s) the material shape is subjected to a blow molding process to achieve a further shaping of the material. The material shape that exits the extruder die(s) may be allowed to cool before it is later re-heated in the blow molding process.
This two part manufacturing process of extruding and later (may be just a few moments later) blow molding the same end product is adaptable for use in the manufacturing of a wide variety of end products. An example of such an end product is a fence post or rail post. It has been known to extrude plastic material to form fence posts and rails for use in decorative and/or protective fences that were traditionally made from wood or metal. A relatively simple die configuration in an extrusion process can be used to extrude a hollow fence post or hollow rail out of plastic or other extrudable material. Likewise, a solid post or rail may be manufactured from an extrusion process with the proper dies, and used in the present invention.
It has been known to create decorative end-caps for fence posts and rail posts in a separate manufacturing process, such as injection molding. Such injection molded end-caps are later assembled in an assembly step to the extruded fence post or rail post. This additional assembly step requires extra time and manpower to complete. Furthermore, the end-caps are susceptible to later becoming disengaged from the fence post or rail post and being lost or damaged.
In one embodiment of the present invention, a hollow fence post or rail post is extruded in a traditional extruder and one end of the extruded post is later placed in a blow mold while air is injected through the other end of the post causing the heated/semi-flowable post material to fill the void created by the blow mold and thereby take the shape of the blow mold cavity as the material cools. The mold itself is later removed and the result is a hollow fence post having a decorative end, all in one-piece construction, requiring no assembly, and having the same aesthetic appearance as the former two step process of assembling a decorative end-cap onto a previously existing fence post or rail post.